Fuses are implemented in various process technology for a variety of different semiconductor IC devices. For example, polysilicon fuses can be used for programming memory devices such as programmable read-only memories (PROM), programmable logic arrays (PLA), and redundancy memory arrays. Fuse arrays are typically formed during the manufacturing of these memory devices, generally formed on a field oxide layer that may be 1 μm or more in thickness. The fuses in the PROM or PLA devices are used to customize it for a specific application. A PROM or PLA device is programmed by opening (or blowing) the appropriate fuses in selected memory cells. In connection with redundancy memory arrays, fuses are used to replace defective memory cells with spare substitute memory cells which were fabricated in the array during the same manufacturing process.
A fuse circuit can also be used by an analog circuit, such as a resistor ladder (resistor trimming network) to adjust circuit's performance. The fuse in this case allows tuning by adjusting a circuit passive parameter by opening one or more links in the resistor ladder.
In order to blow the fuse, which typically comprises a metal or polysilicon body (link) having respective contacts across the link, an electrical method is utilized where a voltage is applied across the link and the current as a result is driven through the link with a current level based the resistance of the link material. Due to resistive heating, the link material heats to beyond its melting point which causes evaporation that results in a break in the link to occur. Polysilicon fuses are known to need less current than a metal fuse to open (break) during programming.
For some ICs there can be a constraint on the field oxide thickness selection to place the fuse on. For one example, the process used may have only a thin field oxide layer (e.g. only 1,000 A (=0.1 μm) of field oxide (FOX)) available. Damaging the FOX layer is a concern during fuse blowing, particularly for thin FOX layer which is most susceptible to damage, because cracking or other physical damage to the FOX layer can be caused by the physical stress occurring during fuse blowing. FOX damage can cause leakage-based IC reliability degradation, such as due to shorting of a contact of the fuse to the silicon substrate through the thin FOX layer under the fuse as a worst case problem.